Soft opening 2-way valve arrangement for a shock absorber

ABSTRACT

Valve arrangement for a shock absorber is described, comprising a valve housing ( 2 ) having a first ( 7 ) and a second port ( 8 ), a pilot chamber ( 3 ) being in fluid communication with the first ( 7 ) and/or second port ( 8 ), wherein a pilot pressure (Pp) is defined by a hydraulic pressure in the pilot chamber ( 3 ). The arrangement further comprises a main valve member ( 4 ) being axially movably arranged in the valve housing ( 2 ) and being arranged to interact with a main valve seat member ( 9 ) in order to restrict a main fluid flow between the first ( 7 ) and second ports ( 8 ) in response to the pilot pressure (Pp) acting on the main valve member ( 4 ). Moreover, the main valve seat member ( 9 ) is movable between a first compression stroke position and a second rebound stroke position so that, during the compression stroke, the main fluid flow is restricted at a first restriction (R 1 ) and a cooperating serially arranged second restriction (R 2 ), and during the rebound stroke, the main fluid flow is restricted at a third restriction (R 3 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

application claims priority to International Application No,PCT/EP2017/053892, filed Feb. 21, 2017 and titled “SOFT OPENING 2-WAYVALVE ARRANGEMENT FOR. A SHOCK ABSORBER,” which in turn claims priorityfrom European Application having Ser. No. 16156682.3, filed Feb. 22,2016 and titled “SOFT OPENING 2-WAY VALVE ARRANGEMENT FOR A SHOCKABSORBER,” both of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the field of valvearrangements. In particular, the present invention relates to a valvearrangement for controlling a flow of damping medium in a shockabsorber.

TECHNICAL BACKGROUND

Generally, within the technical field of shock absorbers that includepilot valves, a pressure regulator, i.e. a valve arrangement, is used tocontrol a flow of damping medium between a compression chamber and arebound chamber during a reciprocal motion of a piston in a dampingmedium filled chamber of the shock absorber. The piston, via a pistonrod, is connected either to a wheel or a chassis, whereas the chamber isconnected to one of the wheel or chassis that the piston is notconnected to. During a compression stroke the piston moves axially in adirection towards the compression chamber and thereby pressurizes thedamping medium in the compression chamber. During a rebound stroke, thepiston moves axially towards the rebound chamber, i.e. in the oppositedirection, and thereby pressurizes the damping medium in the reboundchamber. In accordance with the function of the shock absorber, thepressurized damping medium needs to be transferred from the pressurizedchamber to the other chamber, i.e. from the compression chamber to therebound chamber or vice versa. The flow of damping medium needs to becontrolled to obtain a damping effect of the piston and thus the shockabsorber, i.e. to damp relative motion between the wheel and chassis.

The control of the pressure in the flow of damping medium in the shockabsorber depends on the pressure created by the pilot control valve.Pressure regulators in shock absorbers are usually provided with anaxially movable or deflectable valve member, such as a washer, cone orshim that acts against a seat part. The pressure control is achieved byequilibrium or balance of forces, for example equilibrium between apressure and/or flow force acting on the valve member in one directionand counteracting or opposing forces, such as one or more of a springforce, friction force or pilot pressure force acting on the valve memberin the opposite direction. When the piston of the shock absorber movesat a certain speed such that the pressure and/or flow force becomegreater than the opposing or counteracting forces, the movable valvemember is forced away from the seat part, thereby opening a flowpassage. Thus, the movable valve member is forced to open at a strokedefined as a function of the flow produced by the pressure acting on theregulating area of the pressure regulator.

Traditional valve arrangements of the pressure regulating type describedabove generally have the disadvantage that when a threshold value ofpressure is reached, the valve member is opened and the flow of dampingmedium between the compression chamber and the rebound chamberdramatically increased in a distinct way. This gives a dampingcharacteristic which is not as smooth as desired. Instead, such adamping has a sharp opening with a corner that acts to dynamics thatcommonly causes instabilities such as an initial overshot and followingoscillations.

State of the art valve arrangements for shock absorbers, such as the oneshown in EP0942195B1, have a valve construction that allows a softopening, providing the desired damping characteristics. However,although this solution provides a soft opening in one flow direction,the damping flow in the opposite direction is not at all desirable.Thus, this solution works well in a 1-way valve, but it does not providethe desired damping characteristics in a 2-way valve.

Therefore, there is a need for a 2-way valve arrangement for use inshock absorbers having improved damping characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved 2-way valvearrangement providing improved damping characteristics which aresmoother than prior art.

The invention is based on the inventors' insight that in order for a2-way valve arrangement to have soft opening characteristics the valvearrangement needs restricting interfaces that are different incompression stroke compared to rebound stroke. This realization has alsolead to the surprising effect that the area ratio between thecompression pressure area and the rebound pressure may be set withoutthe prerequisite that the sum of the two areas equals the pilot pressurearea. With other words, the compression pressure area may be increasedwithout decreasing the rebound pressure area, and vice versa. This is anadvantage since the damping characteristics may be even furtherimproved.

Above-mentioned objects are realized through a valve arrangement for ashock absorber, the valve arrangement comprising a valve housingcomprising a first and a second port, a pilot chamber being in fluidcommunication with the first and/or second port, wherein a pilotpressure is defined by a hydraulic pressure in the pilot chamber. Thearrangement further comprises a main valve member being axially movablyarranged in the valve housing and being arranged to interact with a mainvalve seat member in order to restrict a main fluid flow between thefirst and second ports in response to the pilot pressure acting on themain valve member. Moreover, the main valve seat member is movablebetween a first compression stroke position and a second rebound strokeposition so that, during the compression stroke, the main fluid flow isrestricted at a first restriction and a cooperating serially arrangedsecond restriction, and during the rebound stroke, the main fluid flowis restricted at a third restriction.

Hereby, a valve arrangement is provided which has a soft opening duringthe compression stroke, enabled by the two cooperating radial displacedrestrictions being fluidly coupled and serially arranged, and has aregular damping curve during the rebound stroke, enabled by the singlethird restriction. Thus, by letting the rebound flow going through athird restriction, instead of the two cooperating first and secondrestrictions used in the compression stroke, the soft opening may beachieved during the compression stroke, and a regular sharper openingmay be achieved in a rebound stroke. If the rebound would go through thesame restrictions, but in the opposite direction, the damping characterwould not fulfill the desired requirements.

Moreover, in this solution the area ratio between the compression areaand the rebound area may be adjusted without changing the pilot pressurearea. In a solution where the main valve seat is fixed, the sum of thecompression pressured area and rebound pressured area is always equal tothe pilot pressured area. However, with a movable main valve member, itis possible that said sum is greater than the pilot pressured area.Hereby, the valve arrangement may be formed to generate the desireddamping forces in both the compression stroke and the rebound strokewithout compromising with one of the forces.

In the context of this application, any restrictions “cooperating”should be understood as that they are in some way dependent on eachother and work together. E.g. the orifices of two cooperatingrestrictions may be dependent on the same stroke length. Further, in thecontext of this application, e.g. two restrictions being “seriallyarranged” or “arranged in series” should be understood as that the onerestriction is provided upstream of the other restriction. That is,fluid will first go through one restriction and then the otherrestriction, i.e. the fluid is not restricted in two parallelrestrictions.

In one embodiment, the movable main valve seat member is a passivemember and its axial position is controlled by the fluid pressure and/orthe position of the main valve member.

In yet one embodiment, the first restriction is arranged upstreamrelative the second restriction, in view of the compression fluid flowdirection. Thereby, the fluid is first restricted by the firstrestriction and subsequently restricted by the second restriction, whichcontributes to the desired soft opening character of the damper.

In one embodiment, the first and second restrictions are at least partlyformed as circumferential restrictions. In one embodiment the firstrestriction is arranged radially inwards relative the second restrictionHereby, when the restrictions are radially displaced andcircumferentially formed, the orifice of the first restriction willalways be smaller than the orifice of the second restriction when beingat least partly opened.

In yet one embodiment, the first restriction has a smaller orifice thanthe second restriction's orifice when being at least partly opened.

Hereby, when the first and second restrictions are at least partly open,the first restriction is always smaller than the second restriction,which contributes to the desired soft opening character of the damper.

In yet one embodiment, the first restriction and the second restrictionis closed when the main valve seat member is in the rebound strokeposition. Hereby, the first and second restrictions do not affect therebound flow, but the third restriction solely restricts the reboundflow.

In one embodiment, the third restriction is closed when the main valveseat member is in the compression stroke position. Hereby, the thirdrestriction does not affect the compression flow, instead only the firstand second restrictions restrict the compression flow.

In one embodiment the main valve seat member is always arranged tightlyagainst either the main valve member, against the housing or sandwichedbetween the main valve member and the housing. Hereby, either the firstand second restrictions and/or the third restriction are/is closed atdifferent flows.

In one embodiment the main valve seat member is always arranged tightlyagainst the main valve member during compression stroke.

In one embodiment the main valve seat member is always arranged tightlyagainst the housing during the rebound stroke.

In one embodiment, during compression stroke, when the pressure from thefirst port is below a threshold pressure value, the main valve seatmember is sandwiched between the main valve member and the housing.Further, in compression stroke, when the pressure from the first port isabove a threshold pressure value, the main valve seat member is arrangedtightly against the main valve member, but lifted from the valvehousing. Finally, during the rebound stroke the main valve seat memberis arranged tightly against the housing regardless of the pressure levelfrom the second port.

In yet one embodiment, the orifices of the first restriction, secondrestriction and/or third restriction are controlled by means of theaxial position of the main valve member relative the valve housing.

Hereby, the restrictions may be controlled by controlling the axialposition of the main valve member. This may be achieved by e.g.combination forces generated from a pilot pressure, an actuator such asa solenoid and/or spring arrangements.

In yet one embodiment, the valve arrangement comprises a fourthrestriction being arranged in series with the second restriction. In oneembodiment the fourth restriction is arranged in parallel with the firstrestriction. In one embodiment the fourth restriction is arrangedadjacent to the first restriction. All of these embodiments may ofcourse be combined.

In one embodiment, the fourth restriction has a constant orifice beingindependent of the axial position of the main valve member relative thevalve housing. Hereby, a fourth restriction having a set orifice at alltimes is achieved. Thus, the fourth restriction's orifice is strokeindependent. In one embodiment the fourth restriction is arrangedadjacent to the first restriction, so that when the first restriction isat least partly open the first and fourth restrictions act as a commonrestriction. Hereby, the total orifice of the first and fourthrestriction may be larger than the restriction orifice of the secondrestriction in the beginning of a stroke, but smaller than the secondrestriction orifice in a larger stroke. Hereby, the total restrictingcharacter in the compression stroke may be controlled so as tocontribute to the desired soft opening character of the damper.

In yet one embodiment the main fluid flow is restricted by the openingbetween the movable main valve seat member and the main valve memberduring a rebound stroke, and the main fluid flow is restricted by theopening between the movable main valve seat member and the main valvehousing during the compressions stroke.

In yet one embodiment at least one of the valve housing and the movablemain valve seat member further comprises a geometrically definedcircumferential aperture having a radial inner wall and a radial outerwall, wherein the radial inner wall forms a part of the firstrestriction and the radial outer wall forms a part of the secondrestriction.

Hereby, the radial inner and outer wall constitutes the two cooperatingrestrictions achieving the soft opening in the compression stroke.

In one embodiment the circumferential aperture is formed in the valvehousing and the movable valve seat member is sized and adapted tocooperate with the radial inner wall and radial outer wall of thecircumferential aperture to form the first restriction and secondrestriction, so as to restrict the main fluid flow during thecompression stroke.

Hereby, the movable valve seat member may be a simple member, such asfor example a washer. Thereby, the cost for producing the movable valveseat member may be kept low. Further, since the valve housing alreadyhas a rather complex form, it will be formed in a cutting operatingmachine such as e.g. a turning lathe or a milling cutter or similar, andthen forming the additional circumferential aperture will not be ascostly as making the aperture in the movable valve seat member. Thus anoverall cheaper solution may be provided.

In yet one embodiment the movable main valve seat member is a washer ora shim. Hereby, it is possible to provide the movable valve seat memberat a low cost. In the embodiment where the movable valve seat member isa washer it may have a thickness of about 0.5-1.0 mm, preferably about0.7 mm. In the embodiment where the movable valve seat member is a shimit may have a thickness of about 0.1-0.49 mm, preferably about 0.3 mm.

In one embodiment the moveable main valve seat member is a shim. In oneembodiment, said shim has a flexibility allowing its radially outwardend to bend at pressures above a predefined threshold during thecompression stroke, so as to allow a flow of the damping medium withoutmoving the main valve member.

An advantage with having a shim being the movable valve member, is thatduring the compression stroke, the movable valve member's radiallyoutwards end may bend when high pressure pulses of pressure are exertedon the movable valve member, so as to allow a passage of damping mediumthrough the second restriction, without having to move the main valvemember. Hereby, short and intense pressure increases may be handledwithout having to move the main valve member. This further increases thesmoothness of the damping character.

In one embodiment, the moveable main valve seat member is a shim whichis tensioned against the valve housing so that the shims outer end is atleast slightly bent, when the first and second restrictions are closed.Hereby, when the movable valve member is flexible any irregularities inthe movable valve member may be compensated for through flexibility.Thus, the tolerance range may be increased during production.

In one embodiment the movable valve seat member is a washer or shimclosing an upper portion of the circumferential aperture during therebound stroke. Hereby, the movable valve seat member may prevent anymain fluid from flowing past the first and second restrictions.

In yet one embodiment the movable valve seat member is a washer or shimcomprising at least three radial steering projections meshing with themain valve housing. Hereby, the washer/shim may be designed to mesh withthe housing but to prevent non-axial movements of the movable main valvemember. The washer/shim comprises three steering projections so as torestrict the movements of the washer to substantially axial movements.Also, rotational movements around its center axis are permitted. Hereby,any “drawer behavior” may be reduced, i.e. the washer may be preventedto be tilted and locked relative the housing, and thereby it is axiallymovable at all times.

In yet one embodiment the space between the at least three radialsteering projections in the washer/shim form ports for allowing the mainfluid flow during the compression stroke.

In one embodiment, the steering projections and intermediate ports arearranged so that a straight line through any of the projection and thecenter of the washer will also go through an intermediate port. Hereby,jamming is prevented if the washer/shim is tilted (i.e. rotated aroundan axis being perpendicular to its center axis) since there are no twodirectly opposite projections along the diameter of the washer.

In yet one embodiment the valve arrangement further comprise a controlvalve member being movable in an axial direction relative the main valvemember in response to an actuating force acting on the control valvemember, the control valve member being resiliently loaded in an oppositedirection to the actuating force by means of a biasing member, andwherein an interface between the control valve member and the main valvemember comprises an opening restricting an bleed flow of the dampingmedium between the first and second port.

In the context of this application, the bleed flow is to be understoodas a flow of damping medium being parallel to the main fluid flow.Further, the bleed flow is substantially lower flow than the maximummain fluid flow.

Hereby, the arrangement may allow a controlled variable bleed flow,which may be a first stage flow of damping medium. In a compressionstroke, the flow of damping medium from the first to the second portwill substantially go from, in the first stage, being only the bleedflow to mainly be flow through the first and second restrictioncontrolled by the main valve member in a second stage. Hereby, a softopening between the first and second stage is further improved.

In yet one embodiment, the size of the opening restricting the bleedflow in the interface between the control valve member and the mainvalve member is controlled by means of the axial position of the controlvalve member relative the main valve member.

In one embodiment, the main valve seat member comprises a first liftingsurface area arranged to hold the main valve seat member in abutment tothe main valve member in response to a hydraulic pressure in the firstport.

In yet one embodiment, the main valve seat member comprises a secondlifting surface area arranged to hold the main valve seat member inabutment to the main valve housing in response to a hydraulic pressurein the second port.

Further, in one embodiment the main valve member comprises a firstlifting surface area arranged to axially move the main valve memberrelative the valve housing in response to a hydraulic pressure in thefirst port.

In one embodiment the main valve member comprises a second liftingsurface area arranged to axially separate the main valve member from themain valve seat member in response to a hydraulic pressure in the secondport.

In one embodiment, the control valve member is arranged at leastpartially within the main valve member. In yet one embodiment, theactuating force acting on the control valve member is generated by asolenoid.

In one embodiment, the pilot pressure is regulated by a pressureregulator integrated in the control valve member.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and aspect of the present invention will become apparentfrom the following detailed description with reference to accompanyingdrawings, in which:

FIG. 1 shows an exploded view of an embodiment of the valve arrangement

FIG. 2 shows a cross-section of an embodiment when the main valve memberis in a closed position to block a main flow from the first port to thesecond port,

FIG. 3a shows a close-up cross-section of FIG. 2, where the main valvemember is in a closed position to block a main flow from the first portto the second port,

FIG. 3b is a close-up of FIG. 3, but where the main valve member andmain valve seat member is in a partly open position to allow a regulatedmain flow from the first port to the second port, i.e. a flow duringcompression stroke,

FIG. 3c is a close-up of FIG. 3, but where the main valve member is in apartly open position to allow a regulated main flow from the second portto the first port, i.e. a flow during rebound stroke,

FIG. 4a shows a cross-section of a side portion of the main valve seatmember where the lifting surface area during the closed position of themain valve member is illustrated,

FIG. 4b shows a cross-section of a side portion of the main valve seatmember where the lifting surface area during regulated compressionstroke is illustrated,

FIG. 4c shows a top view of the main valve seat member,

FIG. 4d shows a graph over the orifice openings vs. the stroke length,

FIG. 4e shows an illustration of the main valve seat member and thefirst, second and fourth orifices at a given stroke length S, and

FIG. 4f shows a graph over the flow (q) vs. Pressure (P) in threedamping characteristics scenarios.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which currently preferredembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided for thoroughness and completeness, and fully convey the scopeof the invention to the skilled addressee. Like reference charactersrefer to like elements throughout.

FIG. 1 shows a cross-sectional exploded view of a valve arrangement. Thevalve arrangement 1 comprises a valve housing 2. The valve housing hasan upper portion at the top of the figure and a lower portion at thebottom of the figure, which are separated in the figure, but when in usethey are mechanically coupled, e.g. by press fit or a threadedengagement. The arrangement further comprises a main valve member 4 anda control valve member 5, inside the control valve member 5 there is apilot valve member 6 (shown in FIG. 2) acting as a pressure regulator.The valve members are biased inside the housing by biasing means 14, 19(shown as springs). The figure further illustrates the second port 8 inthe lower portion of the valve housing 2. Moreover, the arrangementcomprises the movable main valve seat member 9, which is furtherillustrated in the following figures, especially FIG. 4c . Most detailsin FIG. 1 will be further explained in relation to FIGS. 2-4, wheretheir respective function also will be described. FIG. 1 is mainlyincluded in the application to clarify the form of each component andthereby facilitate the reading and understanding of the application.

FIGS. 2 and 3 a shows a cross-section of an embodiment of the valvearrangement 1 when the main valve member 4 is in a closed position toblock a main flow (not shown) from the first port 7 to the second port8, wherein FIG. 3a is a close-up cross-section of FIG. 2. The valvearrangement 1 comprises a valve housing 2, a pilot chamber 3, a mainvalve member 4, and a control valve member 5. The valve housing 2comprises a first and a second port 7, 8. In the illustrated embodiment,the first and second ports act as inlet and outlet ports, respectively,for inlet and outlet of hydraulic fluid. The pilot chamber 3 is definedby the space formed between the upper surface 41 of the main valvemember and inner walls of the valve housing 2. The pilot chamber 3 is influid communication with the first port 7 via a first axial through hole32 in the main valve member 4 and with the second port 8 via a secondaxial through hole 33 in the main valve member 4. The pilot pressure Ppacting on the upper surface 41 of the main valve member 4 is defined bya hydraulic pressure in the pilot chamber 3.

The main valve member 4 is axially movably arranged in the valve housing2 and is arranged to interact with the movable main valve seat member 9in order to restrict or regulate a pressure in a main fluid flow 10(shown in FIGS. 3b and 3c ) between the first port 7 and the second port8 in response to a pilot pressure Pp acting on an upper surface 41 ofthe main valve member 4. In this embodiment, the main valve member 4 isheld towards the main valve seat member 9 in a closed position. The mainvalve member may be resiliently loaded by any spring members or mayitself be flexible and/or resilient to achieve a desired resilientloading towards the movable main seat valve member 9.

The control valve member 5 is of a substantially cylindrical shape andis arranged coaxially with and partially within the main valve member.The control valve member 5 is furthermore movable in an axial directionrelative the main valve member in response to an actuating force actingon the control valve member. In this embodiment, the actuating force isreceived by an actuating rod 35. The actuating rod may be an axiallymovable magnetic member on which a solenoid exerts a force in responseto an electric current.

Further, the state shown in FIG. 2 may be derived from that either thepressure from port 7 and/or 8 has not yet reached a threshold value whenthe main valve member 4 is lifted towards the pilot chamber 3. Thisthreshold value corresponds to when the lifting force generated from thepressure in any one of the first or second port 7, 8 acts on a liftingareas 42, 43 of the main valve member 4 exceed the counter acting forcefrom the pilot pressure Pp in the pilot chamber 3 acting on the uppersurface 41 of the main valve member 4. This is further explained inrelation to FIGS. 3b and 3c where a regulated main flow 10 isillustrated.

As most clearly illustrated in the close-up shown in FIG. 3a , the mainvalve member comprises a circumferential aperture 25, having a radialinner wall 26 and a radial outer wall 27. In connection with the radialinner wall 26 there is another aperture forming a fourth restrictionR1′. The fourth restriction R1′ allows the damping fluid to enter thecircumferential aperture 25 so as to pressurize the movable main valvemember 9 in response to a pressure in port 7. Further, FIG. 3aillustrates a bleed flow 20 flowing between the first and second portsthrough an opening in the main valve member 4, into the control valvemember 5 and passing along the pilot valve member 6 and then backthrough the control valve member 5 and the main valve member 4. Thisbleed flow is a limited flow which is substantially lower flow than themaximum main fluid flow. The regulated bleed flow 20 corresponds to thefirst stage flow q1 in FIG. 4f , i.e. before the three curves departfrom each other. This will be further elaborated in relation to FIG. 4f.

FIG. 3b is a close-up of FIG. 2, but where the main valve member 4 andmain valve seat member 9 is in a partly open position to allow aregulated main flow 10 from the first port 7 to the second port 8, i.e.a flow during compression stroke. As illustrated, the movable main valvemember 9 and main valve member 4 are held together in a position axiallydisplaced relative the valve housing 2 when compared to the closedposition in FIGS. 2 and 3 a. In this position, a regulated main fluidflow 10 is allowed from the first port 7 to the second port 8, and isrestricted by the first restriction R1 plus the fourth restriction R1′first (upstream, closest to the first port) and then restricted by thesecond restriction R2 downstream of the first restriction R1. The radialinner wall 26 together with the movable valve seat 9 forms a part of thefirst restriction (R1) and the radial outer wall (27) together with themovable valve seat 9 form a part of the second restriction (R2). In anypartly open state the first restriction R1 is smaller than the secondrestriction R2, since the two restrictions are formed as circumferentialrestrictions and being radially displaced. Since the second restrictionhas a larger circumference its orifice will always be larger than theorifice of the first restriction, when formed with a common delimiterupwards (the movable valve seat member 9) and downwards (the radial sidewalls of the housing). Further, the fourth restriction R1′ has aconstant opening. Hereby, the sum of the first R1 and fourth R1′restriction is initially larger than the second restriction R2, but asthe stroke S increases the second restriction becomes larger than thesum of the first and fourth restriction, this is illustrated in FIGS. 4dand 4 e.

Thus, in FIG. 3b a pressure from the damping fluid in port 7 causes theopening axial displacement of the main valve member 4 (acting on thelifting areas 42 and 43) and the main valve seat member 9 (acting on thelifting area 21 a as illustrated in FIG. 4b ). The movement is, asearlier explained, dependent on the counteracting pressure from thepilot chamber 3 acting on the main valve member 4. Hereby, a regulatedmain flow of damping fluid is allowed to flow from the first to thesecond port 7, 8. This type of regulation corresponds to the secondstage flow q1 in FIG. 4f , i.e. after the three curves depart from eachother. Since two serial and cooperative restrictions R1 and R2 are usedto regulate the flow, a soft opening when going from the first stage q1to the second stage q2 may be achieved. This will be further elaboratedin relation to FIG. 4f as mentioned before.

FIG. 3c is also a close-up of the view in FIG. 3, but where the mainvalve member 4 is in a partly open position to allow a regulated mainflow 10 from the second port 8 to the first port 7, i.e. a flow duringrebound stroke. When comparing FIG. 3c to FIG. 3b , it is only themovable main valve seat member 9 that has been moved from being arrangedtightly against the main valve member 4, to instead being arrangedtightly against the valve housing 2. This is achieved through a flow(pressure) of damping from the second port 8 to the first port 7, whichacts on the upper surface, being a lifting area 22, of the movable mainvalve seat member 9 and also acts on the lifting area 43 of the mainvalve member 4, but in an opposite direction so that the main valvemember 4 and the main valve seat member are separated. The pressure inthe second port 8 will always keep the main valve seat member 9 pressedagainst the valve housing 2. Also, depending on the level of pressure,the opening between the main valve member 4 and the main valve seatmember 9 constitutes the third restriction R3. The third restriction R3enables the pressure-regulated flow in rebound stroke.

When comparing FIG. 3b and FIG. 3c , the above-mentioned advantage withhaving a movable valve seat member 9 and thereby getting a more flexiblearea pressure ratio between compression pressure area and reboundpressure area may be understood. In the illustrated embodiment the arearatio between the compression area and the rebound area may be adjustedwithout changing the pilot pressure area. In a solution where the mainvalve seat is fixed, the sum of the compression pressured area andrebound pressured area is equal to the pilot pressured area. However,with a movable main valve member, it is possible that the sum is greaterthan the pilot pressured area, since the movable valve seat member ismoved and thereby the compression pressure and rebound pressure acts atdifferent surfaces. This allows forming the valve arrangement togenerate the desired damping forces in both the compression stroke andthe rebound stroke without compromising with one of the forces.

FIGS. 4a and 4b further illustrates the pressurized areas of the movablevalve seat member 9. In FIG. 4a the pressurized areas 21 b, 21 c and 22corresponds to the area acting on the movable valve seat member 9 whenthe main valve is closed, as illustrated in FIGS. 2 and 3 a. The area 21b corresponds to the portion of the movable valve seat member protrudingfrom the valve housing in a radially inwards direction. The area 21 ccorresponds to the portion of the movable valve seat member arranged ontop of the circumferential aperture 25 in the valve housing. That is,this aperture may be filled with pressurized damping fluid. Further, thearea 22 corresponds to the portion of the movable valve seat member 9extending in a radially outwards direction from the main valve member'sradially outer corner. See FIG. 3 a.

Further, FIG. 4b shows a cross-section of a side portion of the mainvalve seat member where the lifting surface area during regulatedcompression stroke is illustrated. The pressurized area 21 a on themovable valve seat member 9 illustrated is when the main valve member isat least partly opened. The area corresponds to the whole lower surfaceof the movable valve seat member 9.

FIG. 4c illustrates the movable valve seat member 9 from a top view. Itis shown that the movable valve seat member 9 is formed as a washer,with an outer diameter D1 and an inner diameter D2. Furthermore, thewasher comprises three radial steering projections 91. The steeringprojections are sized and adapted to mesh with the main valve housing 2.Furthermore, the space between the at least three radial steeringprojections 91 in the washer forms intermediate ports 92 for allowingthe main fluid flow 10 passing from the first 7 to the second port 8during the compression stroke. The steering projections 91 andintermediate ports 92 in the embodiment are arranged so that not asingle steering projection 91 has an opposing steering projection on theother side of the washer. With other words, a straight line through anyof the projection 91 and the center of the washer will not go through asecond steering 91 projection but instead go through an intermediateport 92. The reason to this design is that jamming of the movable valveseat member 9 may be prevented if it is tilted (i.e. rotated around anaxis being perpendicular to its center axis) since there are no twodirectly opposite projections along the diameter of the washer. It wouldalso be possible to have more radial steering projections, as long asthey are distributed along the circumferential of the movable valve seatmember 9 so as to avoid jamming if it is tilted.

FIG. 4d shows a graph over the orifice openings O_(R1)+O_(R1′) andO_(R2) as a function of the stroke length S. The first orifice O_(R1)corresponds to the orifice of the first restriction R1. This orificeO_(R1) is also illustrated by the envelope surface of the circle in FIG.4e , and denoted with O_(R1), which is thus dependent on the strokelength S. The stroke length is the axial distance between the movablevalve seat member 9 and the main valve housing 2, when being in aregulated position, see for example in FIG. 3b . The second orificeO_(R2) corresponds to the orifice O_(R2) of the second restriction R2.This orifice is also illustrated by the envelope surface of the circlein FIG. 4e , and denoted with O_(R2). The fourth orifice O_(R1′)corresponds to the orifice of the forth restriction R1′. This orificeO_(R1′) is also illustrated by a surface in FIG. 4e denoted withO_(R1′), which corresponds to the opening into the circumferentialaperture in the main valve housing 2. As already explained above, FIG.4e shows an illustration of a cross-sectional side-view of the mainvalve seat member where the first O_(R1), second O_(R2) and fourthO_(R1′) orifices are illustrated at a given stroke length S. From thisillustration it is apparent how the first O_(R1) and second O_(R2)orifices vary with the stroke length S, but the fourth O_(R1′) orificeis static.

In the initial phase of the regulated compression stroke, i.e. when R1and R2 is just opening from a closed position, the restriction will becarried out in the second restriction, which is shown in FIG. 4d , sincethe orifice of the second restriction R2 is smaller than the orifice ofthe first and fourth restriction R1+R1′, in said initial phase. As soonas the orifice of the second restriction R3 is larger than the combinedorifice of the first and fourth restriction R1+R1′, the restriction isinstead carried out at the first and fourth restrictions.

The size relationships between the orifices of the differentrestrictions may vary without departing from the inventive concept. Byadjusting the orifice size relationships, the intersecting point between“O_(R1)+O_(1′)”-curve and the “O_(R2)”-curve the shown in FIG. 4d may bemoved. The orifice size of O_(R1′) is represented by where the“O_(R1)+O_(R1′)”-curve intercepts the Y-axis. The relation between thesize of the first and second restrictions' orifices O_(R1) isillustrated by the different inclinations of the two curves in FIG. 4d .Further, by increasing the relative size of the fourth orifice O_(R1′)relative the maximum orifice size of the first orifice O_(R1) the softopening is prolonged.

The maximum orifice size of the first orifice O_(R1) may be about50%-95% of the maximum orifice size of the second orifice O_(R2). In oneembodiment the maximum orifice size of the first orifice O_(R1) is about70%-90% of the maximum orifice size of the second orifice O_(R2). Inanother embodiment maximum orifice size of the first orifice O_(R1) isabout 75%-85% of the maximum orifice size of the second orifice O_(R2).

The orifice size of the fourth orifice O_(R1′) may be about 0.1%-10% ofthe maximum orifice size of the first orifice O_(R1). In one embodimentthe orifice size of the fourth orifice O_(R1′) is about 0.3%-3% of themaximum orifice size of the first orifice O_(R1). In another embodimentthe orifice size of the fourth orifice O_(R1′) is about 0.5%-1% of themaximum orifice size of the first orifice O_(R1).

Further, as the graph in FIG. 4d illustrates, the combined first andfourth orifices O_(R1) and O_(R1′) are larger than the second orificeO_(R2) during the initial stroke, but at one point, the second orificeO_(R2) is larger than the combined first and fourth orifices O_(R1) andO_(R1′), and increases faster during the same stroke length.

Finally, FIG. 4f shows graph over the pressure P as a function of theflow q in a compression stroke, in three different dampers withdifferent damping characteristics. All functions comprise a common firststage q1, where a regulated bleed flow is illustrated. In the secondstage q2, starting from where the three functions separated from eachother, corresponds to a pressure regulated main fluid flow. The firstdamping character DC1, illustrates a sharp opening, which is the commonbehaviour in 2-way valves today. The second and third functions DC2 andDC3, both illustrate a soft opening, i.e. when the solution described inthis application is used. The difference between the two is the orificesize of the fourth restriction R1′. That is, by altering the size of thefourth restriction's orifice the character of the soft opening may beadjusted. In the second function DC2, the fourth orifice O_(R1′) issmaller than in the third function DC3 which consequently has a largerorifice O_(R1′).

Although exemplary embodiments of the present invention have been shownand described, it will be apparent to the person skilled in the art thata number of changes and modifications, or alterations of the inventionas described herein may be made. Moreover, the different embodimentsdescribed above may be combined in different ways without departing fromthe scope of the inventive concept. Thus, it is to be understood thatthe above description of the invention and the accompanying drawing isto be regarded as a non-limiting example thereof and that the scope ofthe invention is defined in the appended patent claims.

The invention claimed is:
 1. A valve arrangement for a shock absorber,said valve arrangement comprising: a valve housing comprising a firstand a second port; a pilot chamber being in fluid communication withsaid first and/or second port, wherein a pilot pressure is defined by ahydraulic pressure in said pilot chamber; and a main valve member beingaxially movably arranged in said valve housing and being arranged tointeract with a main valve seat member in order to restrict a main fluidflow between said first and second ports in response to said pilotpressure acting on said main valve member; wherein the main valve seatmember is movable between a first compression stroke position and asecond rebound stroke position so that, during the compression stroke,the main fluid flow is restricted at a first restriction and acooperating serially arranged second restriction, and, during therebound stroke, the main fluid flow is restricted at a thirdrestriction, an orifice of said first restriction and an orifice of thesecond restriction is controlled by the axial position of the main valvemember relative the valve housing and wherein at least one of said valvehousing and said movable main valve seat member further comprises ageometrically defined circumferential aperture having a radial innerwall and a radial outer wall, wherein the radial inner wall forms a partof the first restriction and the radial outer wall forms a part of thesecond restriction.
 2. The valve arrangement according to claim 1,wherein the first restriction is arranged upstream relative the secondrestriction, in view of the compression fluid flow direction.
 3. Thevalve arrangement according to claim 1, wherein the first restrictionhas a smaller orifice than the second restriction's orifice when beingat least partly opened.
 4. The valve arrangement according to claim 1,wherein at least one of the first restriction and the second restrictionis closed when said main valve seat member is in said rebound strokeposition.
 5. The valve arrangement according to claim 1, wherein thethird restriction is closed when said main valve seat member is in saidcompression stroke position.
 6. The valve arrangement according to claim1, wherein the orifice of said third restriction is also controlled bythe axial position of the main valve member relative the valve housing.7. The valve arrangement according to claim 1, comprising a fourthrestriction being arranged in series with the second restriction.
 8. Thevalve arrangement according to claim 7, wherein the fourth restrictionhas a constant orifice being independent of the axial position of themain valve member relative the valve housing.
 9. The valve arrangementaccording to claim 1, wherein said circumferential aperture is formed insaid valve housing and the movable valve seat member is sized andadapted to cooperate with the radial inner wall and radial outer wall ofsaid circumferential aperture to form the first restriction and secondrestriction, so as to restrict the main fluid flow during thecompression stroke.
 10. The valve arrangement according to claim 9,wherein the movable valve seat member is a washer or shim.
 11. The valvearrangement according to claim 1, wherein the movable valve seat memberis a washer or shim closing an upper portion of said circumferentialaperture during the rebound stroke.
 12. The valve arrangement accordingto claim 1, wherein the movable valve seat member is a washer or shimcomprising at least three radial steering projections meshing with saidmain valve housing.
 13. The valve arrangement according to claim 12,wherein the space between said at least three steering radialprojections in said washer or shim forms intermediate ports for allowingthe main fluid flow during the compression stroke.
 14. The valvearrangement according to claim 1, further comprising a control valvemember being movable in an axial direction relative said main valvemember in response to an actuating force acting on said control valvemember, said control valve member being resiliently loaded in anopposite direction to said actuating force by means of a biasing member,and wherein an interface between said control valve member and said mainvalve member comprises an opening restricting a bleed flow of thedamping medium between the first and second port.
 15. A valvearrangement for a shock absorber, said valve arrangement comprising: avalve housing comprising a first and a second port˜ a pilot chamberbeing in fluid communication with said first and/or second port, whereina pilot pressure is defined by a hydraulic pressure in said pilotchamber; and a main valve member being axially movably arranged in saidvalve housing and being arranged to interact with a main valve seatmember in order to restrict a main fluid flow between said first andsecond ports in response to said pilot pressure acting on said mainvalve member; wherein the main valve seat member is movable between afirst compression stroke position and a second rebound stroke positionso that, during the compression stroke, the main fluid flow isrestricted at a first restriction and a cooperating serially arrangedsecond restriction, and, during the rebound stroke, the main fluid flowis restricted at a third restriction, and wherein at least one of saidvalve housing and said movable main valve seat member further comprisesa geometrically defined circumferential aperture having a radial innerwall and a radial outer wall, wherein the radial inner wall forms a partof the first restriction and the radial outer wall forms a part of thesecond restriction, and wherein said circumferential aperture is formedin said valve housing and the movable valve seat member is sized andadapted to cooperate with the radial inner wall and radial outer wall ofsaid circumferential aperture to form the first restriction and secondrestriction, so as to restrict the main fluid flow during thecompression stroke.
 16. A valve arrangement for a shock absorber, saidvalve arrangement comprising: a valve housing comprising a first and asecond port; a pilot chamber being in fluid communication with saidfirst and/or second port, wherein a pilot pressure is defined by ahydraulic pressure in said pilot chamber; and a main valve member beingaxially movably arranged in said valve housing and being arranged tointeract with a main valve seat member in order to restrict a main fluidflow between said first and second ports in response to said pilotpressure acting on said main valve member; wherein the main valve seatmember is movable between a first compression stroke position and asecond rebound stroke position so that, during the compression stroke,the main fluid flow is restricted at a first restriction and acooperating serially arranged second restriction, and, during therebound stroke, the main fluid flow is restricted at a thirdrestriction, and wherein at least one of said valve housing and saidmovable main valve seat member further comprises a geometrically definedcircumferential aperture having a radial inner wall and a radial outerwall, wherein the radial inner wall forms a part of the firstrestriction and the radial outer wall forms a part of the secondrestriction, and wherein the movable valve seat member is a washer orshim closing an upper portion of said circumferential aperture duringthe rebound stroke.